Currently, endoscopes or surgical microscopes are extensively used in mildly invasive surgery, but are less commonly used for complex surgical techniques. However, techniques for employing endoscopes or surgical microscopes in more complex surgery have been proposed and are now under development. In these techniques, an image sensor detects images of an object which are then displayed on a display unit while a manipulator is operated to perform microscopic surgery. Prior art optical observation devices for use in surgery include an optical observation device that combines a pupil-separation-type, rigid endoscope with a 3-D observation unit, as disclosed in Japanese Patent Publication No. H06-59199 (corresponding to U.S. Pat. Nos. 5,588,948, and 5,720,706), and in Japanese Patent Publication No. H06-202006 (corresponding to U.S. Pat. No. 5,557,454).
As shown in FIG. 18(a), the pupil-separation-type, rigid endoscope used in such an optical device may be formed of, for example, a rigid part 51 for insertion and a holder part 52 that is connected to the rigid part 51. The rigid part 51 is formed of, in order from the object side, an objective lens 53 having plural lens elements and a relay lens 54 having plural lens groups. The objective lens 53 and the relay lens 54 form an image input optical system which transmits images of object to a beam splitter. The holder part 52 contains a diaphragm 55 containing two apertures 55a, 55b for separating the light transmitted via the image input optical system. Prisms 56, 56′ are used to then direct the light of the right and left light beams, respectively, so as to convey right and left images, respectively. The prisms 56, 56′ have reflecting surfaces 56a, 56′a that are inclined at a 45° angle to the optical axis. These prisms 56, 56′ reflect the right and left light beams, respectively, that enter them via the two apertures 55a, 55b in the diaphragm 55, which is positioned normal to the optical axis. The holder part 52 contains prisms 57, 57′ having reflecting surfaces that reflect the right and left light beams which have been separated by being reflected 90 degrees by the prisms 56, 56′, respectively, so as to be incident onto lenses 58, 58′, respectively, and image sensors such as CCDs 59, 59′, respectively. The CCDs 59, 59′ are positioned at the image planes of the lenses 58, 58′ and they convert the right and left object images, respectively, into electric signals so that the right and left images can be displayed on a monitor via a control unit (not shown).
The imaging optical system S, which includes the holder part 52 as well as the above-discussed components from the apertures 55a, 55b to the CCDs 59, 59′, is rotated as a unit in relation to the rigid part 51. As shown in FIG. 18(b), such a pupil-separation-type, rigid endoscope has a small parallax that is determined by the distance d between the optical axes. The distance d is approximately one-fourth to one-eighth the outer diameter D of the relay lens 54. When such a pupil-separation-type, rigid endoscope is modified for providing a perspective view by making the leading end I of the rigid part 51 shown in FIG. 18(a) have a slanted orientation in relation to the longitudinal direction of the rigid part 51, the imaging optical system S can then be rotated according to the perspective view direction of the leading end I so as to properly orient the image.
The two apertures 55a, 55b formed in the diaphragm 55 can be variable in spacing so as to adjust the parallax magnitude for comfortable observation. Such prior art optical observation devices for use in surgery also include an optical observation device that combines a dual-optical-system-type, rigid endoscope with a 3-D observation unit as disclosed in Japanese Patent Publication No. H06-59199 (which corresponds in subject matter to U.S. Pat. Nos. 5,588,948 and 5,720,706). As shown in FIG. 19(a), the dual-optical-system-type, rigid endoscope used in such optical devices includes, for example, a rigid part 61 for insertion and a holder part 62 that is connected to the rigid part 61. The rigid part 61 contains two image input optical systems 65, 65′ formed of, in order from the object side, objective lenses 63, 63′, each formed of plural lens elements, and relay lenses 64, 64′, each formed of plural lens groups. The holder part 62 includes the following for forming respective object images that are transmitted via each of the two image input optical systems 65, 65′: imaging optical systems formed of prisms 66, 66′ and 67, 67′, imaging lenses 68, 68′, and CCD's 69, 69′. The CCDs 69, 69′ convert the object images transmitted via the two image input optical systems 65, 65′ into electric signals in order to display them on a monitor via a control unit (not shown). Such a dual-optical-system-type, rigid endoscope provides a larger parallax d (FIG. 19(b)) than the pupil-separation-type, rigid endoscope with d being equal to, in this case, approximately one-half the diameter D of the space reserved for the optical system.
Referring back to the pupil-separation-type, rigid endoscope as shown in FIGS. 18(a) and 18(b), although images can be correctly oriented in such a device, there exists a problem in that sufficient parallax magnitude can not be ensured. On the other hand, the dual-optical-system-type, rigid endoscope as is shown in FIG. 19(a) also has some disadvantages. Although the parallax magnitude can be made sufficiently large, the parallax magnitude as well as the parallax direction are fixed. Thus, neither the parallax magnitude nor the parallax direction may be readily adjusted. However, a large parallax may be excessive for some close-up observations, and having the image orientation fixed causes an inconvenience in that images with proper perspective can not be ensured.